1. Field of the Invention
This invention relates to fluid leak testing and in particular to a tester and testing method of determining leakage of pressurized fluid from a container.
2. Description of the Background Art
A common method of determining fluid leakage characteristics of a container is to measure pressure decay following pressurizing of the container with a suitable fluid. It is conventional to utilize air as the pressurizing fluid in many of the testing procedures, as air has the desirable characteristics of being nontoxic, nonflammable, noncorroding and noncontaminating in most instances. By measuring the pressure decay, a quantitative as well as a qualitative indication of the leakage characteristics is obtained. Apparatuses have been developed for automatically measuring such pressure decay with high accuracy and sensitivity.
In one common pressure decay method, the container is pressurized with air from a pressurized air source controlled by an isolation valve. The pressure within the container is monitored during the pressurization step and following the closing of the isolation valve when the desired pressure within the container is reached.
It is conventional in such pressure decay testing to stabilize the pressure by allowing the container to remain with the preselected pressurized fluid therein for a preselected period of time following which the testing of the pressure decay is initiated.
After a second preselected period of time, comprising a test time interval, the pressure within the container is again measured to determine any decrease therein resulting from leakage. One excellent example of a pressure decay leak tester utilizing the above method is that identified as the Himmelstein Model 6500 Pressure Decay Leak Tester, manufactured by the assignee hereof and described in Himmelstein Bulletin 965.
Such testers have an inherent limitation in sensitivity controlled by the sensitivity of the components. The pressure transducer must have sufficient range to accurately measure the operating test pressure. Further, the minimum leak that can be detected by the pressure transducer is determined by the resolution and repeatability of the pressure transducer detector.
The sensitivity of the apparatus is further inversely proportional to the volume of the test item. Thus, an increase in the test volume provides a corresponding decrease in the net pressure change due to a leak.